1. Field of the Invention
The present invention is broadly concerned with improved systems for enhancing oil recovery by increasing the efficiency of injection wells. More particularly, the invention is concerned with a method and corresponding apparatus for operating an injection well having a well bore extending downwardly through geographical strata with higher and lower permeabilities respectively, wherein a downhole booster pump is employed to generate higher and lower pressure output streams which are directed to the lower and higher permeability strata.
2. Description of the Prior Art
When hydrocarbon producing wells are drilled, initial hydrocarbon production is usually attained by natural drive mechanisms (water drive, solution gas, or gas cap, e.g.) which force the hydrocarbons into the producing well bores. If a hydrocarbon reservoir lacks sufficient pore pressure (as imparted by natural drive), to allow natural pressure-driven production, artificial lift methods (pump or gas lift, e.g.) are used to produce the hydrocarbon.
As a large part of the reservoir energy may be spent during the initial (or xe2x80x9cprimaryxe2x80x9d) production, it is frequently necessary to use secondary hydrocarbon production methods to produce the large quantities of hydrocarbons remaining in the reservoir. Water flooding is a widespread technique for recovering additional hydrocarbon and usually involves an entire oil or gas field. Water is injected through certain injection wells selected based on a desired flood pattern and on lithology and geological deposition of the pay interval. Displaced oil is then produced into producing wells in the field.
Advancements in secondary hydrocarbon producing technology has led to several improvements in waterflood techniques. For example, the viscosity of the injected water can be increased using certain polymer viscosifiers (such as polyacrylamides, polysaccharides, and biopolymers) to improve the xe2x80x9csweep efficiencyxe2x80x9d of the injected fluid. This results in greater displacement of hydrocarbons from the reservoir.
The ability to displace oil from all the producing intervals in a hydrocarbon reservoir is limited by the lithological stratification of the reservoir. That is, there are variations in permeability in different geological strata which allow the higher permeability zones to be swept with injected fluid first while leaving a major part of the hydrocarbon saturation in the lower permeability intervals in place. Continued injection of flooding fluid results in xe2x80x9cbreakthroughxe2x80x9d at the producing wells at the high permeability intervals which can render continued injection of the flooding medium uneconomical.
A number of approaches have been used in the past to increase the efficiency of injection well practice and to avoid xe2x80x9cbreakthrough.xe2x80x9d This has involved use of gel treatments to decrease the permeability of a higher permeability strata and thereby improve the sweep efficiency. Attempts have also been made to use polymer gels having selective penetration properties which will preferentially enter high permeability strata. However, these polymers are rare and expensive.
The present invention is broadly directed to systems for operating injection wells having a well bore extending downwardly through geological strata or zones having higher and lower fluid permeabilities, and includes the steps of injecting a fluid into the well bore at a pressure Pi, and using the injected fluid to generate first and second higher and lower pressure output streams at pressures Ph and Pl, respectively, whereupon such streams are directed out of the well bore and into the appropriate geological stratum. In preferred forms, the injected fluid is directed to a fluid-actuated downhole engine and pump assembly, and a first portion of the injected fluid is delivered to the engine which creates work with consequent reduction in the pressure of the first fluid portion to a level below the initial pressure Pi. Some of the created work is transferred to the pump to generate the high pressure output stream. A second portion of the injected fluid is delivered to the pump and is pressurized therein, the pressurized pump output comprising at least a part of the high pressure output stream.
In practice, the engine and pump assembly is located within the well bore proximal to the strata to be treated, typically by placing the assembly within a tubing string. In order to permit passage of the output streams through the geological strata, the well casing is divided with appropriately located and sized output openings.
The preferred engine and pump assembly includes a primary block having a valve chamber, an engine piston chamber, a pump piston chamber, an injected fluid inlet, and high and low pressure fluid delivery outlet openings. The primary block also includes an elongated operator shaft extending along the length of the block from the valve chamber and through the engine and piston pump chambers. This shaft supports an engine piston slidable within the engine chamber and a pump piston slidable within the pump piston chamber. A movable valve member is also located within the valve chamber. In order to direct the incoming injected stream and deliver the desired outputs, the primary block has an injected fluid passageway system operably coupling the valve chamber and the engine piston chamber for alternate delivery of injected fluid into the engine piston chamber on opposite sides of the engine piston, in response to the location of the valve member. This injected fluid passageway system also couples the injected fluid inlet and the pump piston chamber for alternate delivery of injected fluid to the pump piston chamber on opposite sides of the pump piston. The injected fluid passageway system is in communication with the low pressure fluid delivery opening, whereas the high pressure fluid delivery opening of the block is in operative communication with the pump piston chamber.